Reproducibility is one of the main principles of
the scientific
method, and refers to the ability of a test or experiment to be accurately
reproduced, or replicated, by someone else working
independently.

Reproducibility is different from repeatability, which
measures the success rate in successive experiments, possibly
conducted by the same experimenters. Reproducibility relates to the
agreement of test results with different operators, test apparatus,
and laboratory locations. It is often reported as a standard
deviation.

While repeatability of scientific experiments is
desirable, it is not considered necessary to establish the
scientific validity of a theory. For example, the cloning of animals is difficult
to repeat, but has been reproduced by various teams working
independently, and is a well established research domain. One
failed cloning does not mean that the theory is wrong or
unscientific. Repeatability is often low in protosciences.

The results of an experiment performed by a
particular researcher
or group of researchers are generally evaluated by other
independent researchers by reproducing the original experiment.
They repeat the same experiment themselves, based on the original
experimental description, and see if their experiment gives similar
results to those reported by the original group. The result values
are said to be commensurate if they are obtained (in distinct
experimental trials) according to the same reproducible
experimental description and procedure.

The basic idea can be seen in Aristotle's
dictum that there is no scientific knowledge of the individual,
where the word used for individual in Greek had the connotation of
the idiosyncratic, or wholly isolated occurrence. Thus all
knowledge, all science, necessarily involves the formation of
general concepts and the invocation of their corresponding symbols
in language (cf. Turner).

Famous problems

In March 1989, University
of Utah chemists Stanley Pons and Martin Fleischmann reported
the production of excess heat that could only be explained by a
nuclear process. The report was astounding given the simplicity of
the equipment: it was essentially an electrolysis cell
containing heavy water
and a palladiumcathode which rapidly
absorbed the deuterium
produced during electrolysis. The news media reported on the
experiments widely, and it was a front-page item on many newspapers
around the world. Over the next several months others tried to
replicate the experiment, but were unsuccessful. At the end of May
the US Energy Research Advisory Board found the evidence to be
unconvincing, and cold fusion
was dismissed as pseudoscience. Later on,
successful replications by independent teams were reported in peer
reviewed scientific journals, and, although the effect is not
considered fully repeatable, the field eventually gained some
scientific recognition.

In the 1930's the Austrian scientist Wilhelm
Reich claimed to have discovered a physical energy he called
"orgone," and which he
said existed in the atmosphere and in all living matter. He
developed instruments to detect and harness this energy that he
said could be used to treat illness or control the weather. His
views were not accepted by the mainstream scientific community; in
fact, he was vilified for his claims. In the early 1940's Reich
encouraged Albert
Einstein to test an orgone accumulator, which Einstein did, but
he disagreed on the interpretation of the results. In 2001,
Canadian researchers Paulo Correa and Alexandra Correa claimed to
have successfully reproduced the experiment. But Martin
Gardner's book,
Fads and Fallacies in the Name of Science debunks orgone
energy.

Nikola Tesla
claimed as early as 1899 to have used a high frequency current to
light gas-filled lamps from over away without
using wires. In 1904 he built Wardenclyffe
Tower on Long
Island to demonstrate means to send and receive power without
connecting wires. The facility was never fully operational and was
not completed, supposedly due to economic problems. Tesla's
experiments have never been replicated.